Abstract
Environmental protection is becoming more important and heat pumps with natural working fluids are being developed eagerly. On the other hand, in Japan, the demand for hot tap water accounts for about one third of residential final energy consumption, but most of this demand is met by direct combustion of fossil fuel. So it is very effective for saving energy to develop highly efficient heat pumps for hot tap water supply. Under such a circumstance, the development of CO2 heat pump water heater for residential use was started. The components, such as a compressor, heat exchangers etc. were developed. The prototype, which consists of these components, was designed and made. In this paper, we describe the outline of the prototype heat pump unit and its experimental results including its characteristic and performance. Also the yearly average COP on Tokyo condition was estimated from these studies and it was clarified that the average COP was over 3. The developed CO2 heat pump water heater can achieve high efficiency and is very promising.
